1. Field of the Invention
The present invention relates to an electrically powered drive apparatus for controlling, for example, the opening of the throttle valve of a vehicle and more particularly to a clutch apparatus incorporated in the electrically powered drive apparatus.
2. Prior Art
FIG. 3 and FIGS. 4A-4B illustrate an electrically powered drive apparatus disclosed by Japanese Patent KOKAI No. 62-203766. FIG. 3 shows a cross-sectional view of the apparatus and FIG. 4A and FIG. 4B show enlarged fragmentary views of the clutch apparatus 11. The electrically powered drive apparatus is mounted to a mounting plate 26. A rotary lever 16 is secured to an output shaft 10. An external load-driving wire 18 is disposed at its one end about the rotary lever 16 and extends at its other end to for example a throttle valve (not shown). The rotary lever 16 is basically formed by a circular member having a groove for receiving the wire 18 on its external circumference. The reference numerals 3, 4, 5, 6 and 7 denote a train of reduction gears. When the clutch 11 engages, the rotary lever 16 winds up or releases the wire 18 depending on the direction of rotation of a motor 1. The reference numeral 14 denotes a clutch yoke. One of the clutch plates 13 is secured to the output shaft 10, while the other clutch plate 8 is mounted on a gear 7 which is loosely fitted on the output shaft 10.
A plurality of pins 12 are provided on the clutch plate 13. When a clutch coil 15 is energized, the ferrite clutch plate 8 is attracted as shown in FIG. 4B, to cause a plurality of pins 12 to engage with a plurality of teeth 8a, thereby transmitting the drive force of the gear 7 to the output shaft 10. A return spring 9 ensures that the clutch plate 8 disengages from the mating clutch plate 13 when the clutch coil 15 is de-energized.
When the motor 1 is operated, the clutch plate 8 is rotated by the motor 1 through the train of the reduction gears 3-7. If the clutch apparatus 11 is in the OFF position, then the motor torque is not transmitted to the output shaft 10. When the clutch apparatus 11 is in the ON position, that is, when the clutch coil 15 is energized, the clutch plate 8 engages the clutch plate 13 to transmit the motor torque to the output shaft. The clutch apparatus 11 of such a prior art electrically powered drive apparatus may be operated, in some cases, to engage or disengage with the motor 1 being operated; therefore the clutch plate 8 that has a plurality of teeth 8a must have good mechanical strength so that it can withstand a large impact when the pins 12 are driven into engagement with or disengagement from the teeth 8a. In the mean time, the ferrite clutch plate 8, as a magnetic member, must be suitably attracted by the clutch coil 15 for sure clutch engagement.
Conventionally, the ferrite clutch plate 8 is made of a ferrite material which is quenched through cementation for increased mechanical strength, and the thickness of the clutch plate 8 is increased to compensate for a decrease in magnetic efficiency due to the quenching to thereby maintain a sufficient amount of effective magnetic flux therethrough. Thus, when manufacturing the clutch plate through pressing, a large deformation will result, particularly at an edge portion thereof, which necessitates the pins 12 to fit the teeth 8a, across the entire thickness of the member to ensure an effective fitting length of the pin 12 into the tooth 8a. This causes a large gap between the clutch plate 8 and the clutch coil 15, leading to a bulky, large size of the clutch coil 15. The prior art, thus described, is necessarily of a large size.